Vascular embolization with an expansible implant

ABSTRACT

A vascular implant formed of a compressible foam material has a compressed configuration from which it is expansible into a configuration substantially conforming to the shape and size of a vascular site to be embolized. Preferably, the implant is formed of a hydrophilic, macroporous foam material, having an initial configuration of a scaled-down model of the vascular site, from which it is compressible into the compressed configuration. The implant is made by scanning the vascular site to create a digitized scan data set; using the scan data set to create a three-dimensional digitized virtual model of the vascular site; using the virtual model to create a scaled-down physical mold of the vascular site; and using the mold to create a vascular implant in the form of a scaled-down model of the vascular site. To embolize a vascular site, the implant is compressed and passed through a microcatheter, the distal end of which has been passed into a vascular site. Upon entering the vascular site, the implant expands in situ substantially to fill the vascular site. A retention element is contained within the microcatheter and has a distal end detachably connected to the implant. A flexible, tubular deployment element is used to pass the implant and the retention element through the microcatheter, and then to separate the implant from the retention element when the implant has been passed out of the microcatheter and into the vascular site.

CROSS REFERENCE TO RELATED APPLICATION

[0001] Not Applicable

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable

BACKGROUND OF THE INVENTION

[0003] The present invention relates to the field of methods and devicesfor the embolization of vascular aneurysms and similar vascularabnormalities. More specifically, the present invention relates to (a)an expansible vascular implant that is inserted into a vascular sitesuch as an aneurysm to create an embolism therein; (b) a method ofmaking the expansible implant; and (c) a method and an apparatus forembolizing a vascular site using the implant.

[0004] The embolization of blood vessels is desired in a number ofclinical situations. For example, vascular embolization has been used tocontrol vascular bleeding, to occlude the blood supply to tumors, and toocclude vascular aneurysms, particularly intracranial aneurysms. Inrecent years, vascular embolization for the treatment of aneurysms hasreceived much attention. Several different treatment modalities havebeen employed in the prior art. U.S. Pat. No. 4,819,637-Dormandy, Jr. etal., for example, describes a vascular embolization system that employsa detachable balloon delivered to the aneurysm site by an intravascularcatheter. The balloon is carried into the aneurysm at the tip of thecatheter, and it is inflated inside the aneurysm with a solidifyingfluid (typically a polymerizable resin or gel) to occlude the aneurysm.The balloon is then detached from the catheter by gentle traction on thecatheter. While the balloon-type embolization device can provide aneffective occlusion of many types of aneurysms, it is difficult toretrieve or move after the solidifying fluid sets, and it is difficultto visualize unless it is filled with a contrast material. Furthermore,there are risks of balloon rupture during inflation and of prematuredetachment of the balloon from the catheter.

[0005] Another approach is the direct injection of a liquid polymerembolic agent into the vascular site to be occluded. One type of liquidpolymer used in the direct injection technique is a rapidly polymerizingliquid, such as a cyanoacrylate resin, particularly isobutylcyanoacrylate, that is delivered to the target site as a liquid, andthen is polymerized in situ. Alternatively, a liquid polymer that isprecipitated at the target site from a carrier solution has been used.An example of this type of embolic agent is a cellulose acetate polymermixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO).Another type is ethylene glycol copolymer dissolved in DMSO. On contactwith blood, the DMSO diffuses out, and the polymer precipitates out andrapidly hardens into an embolic mass that conforms to the shape of theaneurysm. Other examples of materials used in this “direct injection”method are disclosed in the following U.S. Pat. Nos.: 4,551,132-Pásztoret al.; 4,795,741-Leshchiner et al.; 5,525,334-Ito et al.; and5,580,568-Greff et al.

[0006] The direct injection of liquid polymer embolic agents has provendifficult in practice. For example, migration of the polymeric materialfrom the aneurysm and into the adjacent blood vessel has presented aproblem. In addition, visualization of the embolization materialrequires that a contrasting agent be mixed with it, and selectingembolization materials and contrasting agents that are mutuallycompatible may result in performance compromises that are less thanoptimal. Furthermore, precise control of the deployment of the polymericembolization material is difficult, leading to the risk of improperplacement and/or premature solidification of the material. Moreover,once the embolization material is deployed and solidified, it isdifficult to move or retrieve.

[0007] Another approach that has shown promise is the use ofthrombogenic microcoils. These microcoils may be made of a biocompatiblemetal alloy (typically platinum and tungsten) or a suitable polymer. Ifmade of metal, the coil may be provided with Dacron fibers to increasethrombogenicity. The coil is deployed through a microcatheter to thevascular site. Examples of microcoils are disclosed in the followingU.S. Pat. Nos.: 4,994,069-Ritchart et al.; 5,133,731-Butler et al.;5,226,911-Chee et al.; 5,312,415-Palermo; 5,382,259-Phelps et al.;5,382,260-Dormandy, Jr. et al.; 5,476,472-Dormandy, Jr. et al.;5,578,074-Mirigian; 5,582,619-Ken; 5,624,461-Mariant; 5,645,558-Horton;5,658,308-Snyder; and 5,718,711-Berenstein et al.

[0008] The microcoil approach has met with some success in treatingsmall aneurysms with narrow necks, but the coil must be tightly packedinto the aneurysm to avoid shifting that can lead to recanalization.Microcoils have been less successful in the treatment of largeraneurysms, especially those with relatively wide necks. A disadvantageof microcoils is that they are not easily retrievable; if a coilmigrates out of the aneurysm, a second procedure to retrieve it and moveit back into place is necessary. Furthermore, complete packing of ananeurysm using microcoils can be difficult to achieve in practice.

[0009] A specific type of microcoil that has achieved a measure ofsuccess is the Guglielmi Detachable Coil (“GDC”). The GDC employs aplatinum wire coil fixed to a stainless steel guidewire by a solderconnection. After the coil is placed inside an aneurysm, an electricalcurrent is applied to the guidewire, which heats sufficiently to meltthe solder junction, thereby detaching the coil from the guidewire. Theapplication of the current also creates a positive electrical charge onthe coil, which attracts negatively-charged blood cells, platelets, andfibrinogen, thereby increasing the thrombogenicity of the coil. Severalcoils of different diameters and lengths can be packed into an aneurysmuntil the aneurysm is completely filled. The coils thus create and holda thrombus within the aneurysm, inhibiting its displacement and itsfragmentation.

[0010] The advantages of the GDC procedure are the ability to withdrawand relocate the coil if it migrates from its desired location, and theenhanced ability to promote the formation of a stable thrombus withinthe aneurysm. Nevertheless, as in conventional microcoil techniques, thesuccessful use of the GDC procedure has been substantially limited tosmall aneurysms with narrow necks.

[0011] Still another approach to the embolization of an abnormalvascular site is the injection into the site of a biocompatiblehydrogel, such as poly (2-hydroxyethyl methacrylate) (“pHEMA” or“PHEMA”); or a polyvinyl alcohol foam (“PAF”). See, e.g., Horák et al.,“Hydrogels in Endovascular Embolization. II. Clinical Use of SphericalParticles”, Biomaterials, Vol. 7, pp. 467-470 (November, 1986); Rao etal., “Hydrolysed Microspheres from Cross-Linked PolymethylMethacrylate”, J. Neuroradiol., Vol. 18, pp. 61-69 (1991); Latchaw etal., “Polyvinyl Foam Embolization of Vascular and Neoplastic Lesions ofthe Head, Neck, and Spine”, Radiology, Vol. 131, pp. 669-679 (June,1979). These materials are delivered as microparticles in a carrierfluid that is injected into the vascular site, a process that has provendifficult to control.

[0012] A further development has been the formulation of the hydrogelmaterials into a preformed implant or plug that is installed in thevascular site by means such as a microcatheter. See, e.g., U.S. Pat.Nos. 5,258,042-Mehta and 5,456,693-Conston et al. These types of plugsor implants are primarily designed for obstructing blood flow through atubular vessel or the neck of an aneurysm, and they are not easilyadapted for precise implantation within a sack-shaped vascularstructure, such as an aneurysm, so as to fill substantially the entirevolume of the structure.

[0013] There has thus been a long-felt, but as yet unsatisfied need foran aneurysm treatment device and method that can substantially fillaneurysms of a large range of sizes, configurations, and neck widthswith a thrombogenic medium with a minimal risk of inadvertent aneurysmrupture or blood vessel wall damage. There has been a further need forsuch a method and device that also allow for the precise locationaldeployment of the medium, while also minimizing the potential formigration away from the target location. In addition, a method anddevice meeting these criteria should also be relatively easy to use in aclinical setting. Such ease of use, for example, should preferablyinclude a provision for good visualization of the device during andafter deployment in an aneurysm.

SUMMARY OF THE INVENTION

[0014] Broadly, a first aspect of the present invention is a device foroccluding a vascular site, such as an aneurysm, comprising a conformalvascular implant, formed of an expansible material, that is compressiblefrom an initial configuration for insertion into the vascular site bymeans such as a microcatheter while the implant is in a compressedconfiguration, and that is expansible in situ into an expandedconfiguration in which it substantially fills the vascular site, therebyto embolize the site, wherein the initial configuration of the implantis a scaled-down model of the vascular site.

[0015] In a preferred embodiment, the implant is made of a hydrophilic,macroporous, polymeric, hydrogel foam material, in particular awater-swellable foam matrix formed as a macroporous solid comprising afoam stabilizing agent and a polymer or copolymer of a free radicalpolymerizable hydrophilic olefin monomer cross-linked with up to about10% by weight of a multiolefin-functional cross-linking agent. Thematerial is modified, or contains additives, to make the implant visibleby conventional imaging techniques.

[0016] Another aspect of the present invention is a method ofmanufacturing a vascular implant, comprising the steps of: (a) imaging avascular site by scanning the vascular site to create a digitized scandata set; (b) using the scan data set to create a three-dimensionaldigitized virtual model of the vascular site; and (c) forming a vascularimplant device in the form of a physical model of the vascular site,using the virtual model, the implant being formed of a compressible andexpansible biocompatible foam material. In a specific embodiment, theforming step (c) comprises the substeps of: (c)(1) using the virtualmodel to create a scaled-down, three-dimensional physical mold of thevascular site; and (c)(2) using the mold to create a vascular implant inthe form of a scaled-down physical model of the vascular site.

[0017] In the preferred embodiment of the method of manufacturing theimplant, the imaging step is performed with a scanning technique such ascomputer tomography (commonly called “CT” or “CAT”), magnetic resonanceimaging (MRI), magnetic resonance angiography (MRA), or ultrasound.Commercially-available software, typically packaged with and employed bythe scanning apparatus, reconstructs the scan data set created by theimaging into the three-dimensional digitized model of the vascular site.The digitized model is then translated, by commercially-availablesoftware, into a form that is useable in a commercially availableCAD/CAM program to create the scaled-down physical mold by means ofstereolithography. A suitable implant material, preferably a macroporoushydrogel foam material, is injected in a liquid or semiliquid state intothe mold. Once solidified, the hydrogel foam material is removed fromthe mold as an implant in the form of a scaled-down physical model ofthe vascular site.

[0018] A third aspect of the present invention is a method forembolizing a vascular site, comprising the steps of: (a) passing amicrocatheter intravascularly so that its distal end is in a vascularsite; (b) providing a vascular implant in the form of a scaled-downphysical model of the vascular site, the implant being formed of acompressible and expansible biocompatible foam material; (c) compressingthe implant into a compressed configuration dimensioned to pass througha microcatheter; (d) passing the implant, while it is in its compressedconfiguration, through the microcatheter so that the implant emergesfrom the distal end of the microcatheter into the vascular site; and (e)expanding the implant in situ substantially to fill the vascular site.

[0019] The apparatus employed in the embolization method comprises anelongate, flexible deployment element dimensioned to fit axially withinan intravascular microcatheter; a filamentous implant retention elementdisposed axially through the deployment element from its proximal end toits distal end; and an implant device removably attached to the distalend of the retention element.

[0020] The implant device, in its preferred embodiment, is formed of amoldable, hydrophilically expansible, biocompatible foam material thathas an initial configuration in the form of a scaled-down physical modelof the vascular site, that is compressible into a compressedconfiguration that fits within the microcatheter, and that ishydrophilically expansible into an expanded configuration in which it isdimensioned substantially to conform to and fill the vascular site.Alternatively, the implant device may be formed of a non-hydrophilicfoam material having an initial configuration that is substantially thesame size and shape as the vascular site, and that restores itself toits initial configuration after it is released from its compressedconfiguration.

[0021] The retention element is preferably a flexible wire having adistal end configured to releasably engage the implant device while theimplant device is in its compressed configuration, thus to retain theimplant device within the distal end of the microcatheter while thedistal end of the microcatheter is inserted into the vascular site. Thewire is movable axially with the deployment element in the distaldirection to expose the implant from the distal end of themicrocatheter, and is movable proximally with respect to the deploymentelement to urge the implant device against the distal end of thedeployment element, thereby push the implant device off of the wire.Thus released into the vascular site, the implant device expands into anexpanded configuration in which it substantially conforms to and fillsthe vascular site.

[0022] The present invention provides a number of significantadvantages. Specifically, the present invention provides an effectivevascular embolization implant that can be deployed within a vascularsite with excellent locational control, and with a lower risk ofvascular rupture, tissue damage, or migration than with prior artimplant devices. Furthermore, the implant device, by being modelled onthe actual vascular site in which it is to be implanted, effects aconformal fit within the site that promotes effective embolization, andyet its ability to be delivered to the site in a highly compressedconfiguration facilitates precise and highly controllable deploymentwith a microcatheter. In addition, the method of fabricating the implantdevice, by modeling it on each individual site, allows implant devicesto be made that can effectively embolize vascular sites having a widevariety of sizes, configurations, and (in the particular case ofaneurysms) neck widths. These and other advantages will be readilyappreciated from the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a flow chart showing a method of manufacturing avascular implant in accordance with a preferred embodiment of themanufacturing method aspect of the present invention;

[0024]FIG. 2 is a perspective view of a vascular implant in accordancewith a preferred embodiment of the vascular implant device aspect of thepresent invention, showing the implant in its initial configuration;

[0025]FIG. 3 is an elevational view of the implant of FIG. 2, showingthe implant in its compressed configuration;

[0026]FIG. 4 is a perspective view of the implant of FIG. 2, showing theimplant in its expanded configuration;

[0027]FIG. 5 is a cross-sectional view of an implanting apparatusemployed in a method of embolizing a vascular site in accordance with apreferred embodiment of the embolizing method aspect of the presentinvention; and

[0028]FIGS. 6 through 10 are semischematic views showing the steps in amethod of embolizing a vascular site (specifically, an aneurysm) inaccordance with a preferred embodiment of the embolizing method aspectof the present invention.

DETAILED DESCRIPTION OF THE INVENTION The Method of Manufacturing aVascular Implant

[0029] A first aspect of the present invention is a method ofmanufacturing a vascular implant device. The steps of a preferredembodiment of the manufacturing method are shown as a sequence ofdescriptive boxes in the flow chart of FIG. 1.

[0030] The first step, shown in box 10 of FIG. 1, is the step ofcreating an image of a vascular site, such as an aneurysm, in which anembolizing implant is to be installed. This imaging step is performed byscanning the site using any of several conventional imaging techniques,such as computer tomography, magnetic resonance imaging (MRI), magneticresonance angiography (MRA), or ultrasound.

[0031] The result of the imaging step is a digitized scan data set thatis stored in a computer memory, from which the data set is retrieved foroperation of the next step: computerized reconstruction of athree-dimensional digitized virtual model of the vascular site (box 12of FIG. 1). This step of creating a three-dimensional digital model istypically performed by software designed for this purpose that ispackaged with and employed by the imaging apparatus.

[0032] The digitized, three-dimensional virtual model is then translatedinto a form in which it can be employed in a commercially-availableCAD/CAM program (box 14) which controls a stereolithography process (box16) to create a mold for forming an implant device. The translation ofthe virtual model is performed by software that is commerciallyavailable, for example, from Cyberform International, Inc., ofRichardson, Tex., and from Stratasys, Inc., of Minneapolis, Minn. Themold (not shown) is preferably scaled-down from the dimensions of thevascular site, with a scale of about 1:2 to about 1:6, with about 1:4being preferred. Alternatively, the mold may be made “life size” (i.e.,1:1); that is, a full-size or nearly full-size replica of the vascularsite. The mold is used in the fabrication of a vascular implant deviceby conventional molding techniques (box 18).

The Implant Device

[0033] A vascular implant device 20, in accordance with the presentinvention, is shown in FIG. 2 as it appears in its uncompressed orprecompressed initial configuration after withdrawal from the mold.Preferably, the implant device 20 is molded directly onto the distal endportion of an elongate, flexible, filamentous retention element, such asa retention wire 22, for purposes to be described below. The retentionwire 22 preferably has a distal end that terminates in a knob 24 (FIG.5) for better retention of the implant device 20 thereon.

[0034] In the preferred embodiment, the implant device 20 is made of abiocompatible, macroporous, hydrophilic hydrogel foam material, inparticular a water-swellable foam matrix formed as a macroporous solidcomprising a foam stabilizing agent and a polymer or copolymer of a freeradical polymerizable hydrophilic olefin monomer cross-linked with up toabout 10% by weight of a multiolefin-functional cross-linking agent. Asuitable material of this type is described in U.S. Pat. No.5,570,585-Park et al., the disclosure of which is incorporated herein byreference. Another suitable material is a porous hydrated polyvinylalcohol foam (PAF) gel prepared from a polyvinyl alcohol solution in amixed solvent consisting of water and a water-miscible organic solvent,as described, for example, in U.S. Pat. No. 4,663,358-Hyon et al., thedisclosure of which is incorporated herein by reference. Still anothersuitable material is PHEMA, as discussed in the references cited above.See, e.g., Horak et al., supra, and Rao et al., supra. The foam materialpreferably has a void ratio of at least about 90%, and its hydrophilicproperties are such that it has a water content of at least about 90%when fully hydrated.

[0035] In a preferred embodiment, the implant device 20, in its initial,precompressed configuration, will have the same configuration as thevascular site, but it will be smaller, by a factor of approximately twoto approximately six. The material of the implant device 20, and itsinitial size, are selected so that the implant device 20 is swellable orexpansible to approximately the size of the vascular site, primarily bythe hydrophilic absorption of water molecules from blood plasma, andsecondarily by the filling of its pores with blood. The result is anexpanded configuration for the implant device 20, as shown in FIG. 4,that is large enough substantially to fill the vascular site.

[0036] Alternatively, the implant 20 device can be molded so that in itsinitial, precompressed configuration, it is “life size”, i.e.,approximately the same size as the vascular site. In this case, thepreferred material is a compressible, non-hydrophilic polymeric foammaterial, such as polyurethane. In actual clinical practice, anon-hydrophilic implant device 20 would advantageously be made slightlysmaller than actual life size, to accommodate swelling due to thefilling of the pores.

[0037] The foam material of the implant device 20, whether hydrophilicor non-hydrophilic, is advantageously modified, or contains additives,to make the implant 20 visible by conventional imaging techniques. Forexample, the foam can be impregnated with a water-insoluble radiopaquematerial such as barium sulfate, as described by Thanoo et al.,“Radiopaque Hydrogel Microspheres”, J. Microencapsulation, Vol. 6, No.2, pp. 233-244 (1989). Alternatively, the hydrogel monomers can becopolymerized with radiopaque materials, as described in Horák et al.,“New Radiopaque PolyHEMA-Based Hydrogel Particles”, J. BiomedicalMaterials Research, Vol. 34, pp. 183-188 (1997).

[0038] Whatever the material from which the implant device 20 is made,the implant device 20 must be compressible to a fraction of its initialsize, preferably into a substantially cylindrical or lozenge-shapedconfiguration, as shown in FIG. 3. Compression of the implant device 20can be performed by squeezing it or crimping it with any suitablefixture or implement (not shown), and then “setting” it in itscompressed configuration by heating and/or drying, as is well-known. Thepurpose for this compression will be explained below in connection withthe method of using the implant device 20 to embolize a vascular site.

The Method and Apparatus for Embolizing a Vascular Site

[0039] The method of embolizing a vascular site using the implant device20 is performed using an implanting apparatus 30, a preferred embodimentof which is shown in FIG. 5. The implanting apparatus 30 comprises theretention element or wire 22, a microcatheter 32, and an elongate,flexible, hollow, tubular element 34 (preferably a coil) that functionsas an implant deployment element, as will be described below. With theimplant device 20 attached to the distal end of the retention wire 22,the proximal end of the retention wire 22 is inserted into the distalend of the implant deployment element 34 and threaded axially throughthe implant deployment element 34 until the proximal end of the implantdevice 20 seats against, or is closely adjacent to, the distal end ofthe implant deployment element 34. The implant deployment element 34 isdimensioned for passing axially through the microcatheter 32. Thus, theimplant deployment element 34, with the implant device 20 extending fromits proximal end, may be inserted into the proximal end (not shown) ofthe microcatheter 32 and passed axially therethrough until the implantdevice 20 emerges from the distal end of the microcatheter 32, as shownin FIG. 5.

[0040] The implant device 20, in its compressed configuration, has amaximum outside diameter that is less than the inside diameter of themicrocatheter 32, so that the implant device 20 can be passed throughthe microcatheter 32. The implant device 20 is preferably compressed and“set”, as described above, before it is inserted into the microcatheter32.

[0041]FIGS. 6 through 10 illustrate the steps employed in the method ofembolizing a vascular site 40 using the implant device 20. The vascularsite 40 shown in the drawings is a typical aneurysm, but the inventionis not limited to any particular type of vascular site to be embolized.

[0042] First, as shown in FIG. 6, the microcatheter 32 is threadedintravascularly, by conventional means, until its distal end is situatedwithin the vascular site 40. This threading operation is typicallyperformed by first introducing a catheter guidewire (not shown) alongthe desired microcatheter path, and then feeding the microcatheter 32over the catheter guidewire until the microcatheter 32 is positionedsubstantially as shown in FIG. 6. The catheter guidewire is thenremoved.

[0043] The implant deployment element 34, with the implant device 20extending from its distal end, is then passed through the microcatheter32, as described above, until the implant device 20 emerges from thedistal end of the microcatheter 32 into the vascular site 40, as shownin FIGS. 7 and 8. When inserting the implant device 20 into themicrocatheter 32, a biocompatible non-aqueous fluid, such aspolyethylene glycol, may be injected into the microcatheter 32 toprevent premature expansion of the implant device 20 due to hydration,and to reduce friction with the interior of the microcatheter 32. Theimplant device 20 thus being exposed from the microcatheter 32 into theinterior of the vascular site 40, the pores of the implant device 20begin to absorb aqueous fluid from the blood within the vascular site 40to release its “set”, allowing it to begin assuming its expandedconfiguration, as shown in FIG. 9. Then, if the implant device 20 is ofa hydrophilic material, it continues to expand due to hydrophilichydration of the implant material, as well as from the filling of itspores with blood. If the implant device 20 is of a non-hydrophilicmaterial, its expansion is due to the latter mechanism only.

[0044] Finally, when the expansion of the implant device 20 is wellunderway (and not necessarily when it is completed), the retention wire22 is pulled proximally with respect to the implant deployment element34, causing the implant device to be pushed off the end of theinstallation wire 22 by means of the pressure applied to it by thedistal end of the implant deployment element 34. The implant device 20,now free of the implanting apparatus 30, as shown in FIG. 10, maycontinue to expand until it substantially fills the vascular site 40.The implanting apparatus 30 is then removed, leaving the implant device20 in place to embolize the vascular site 40.

[0045] While a preferred embodiment of the invention has been describedabove, a number of variations and modifications may suggest themselvesto those skilled in the pertinent arts. For example, instead ofcustom-fabricating the implant device for each patient, implant devicesin a variety of “standard” sizes and shapes may be made, and aparticular implant device then selected for a patient based on theimaging of the vascular site. In this case, the fabrication method shownin FIG. 1 would be modified by first creating a three-dimensionaldigital model for each standardized implant, (box 12), and thenproceeding with the subsequent steps shown in boxes 14, 16, and 18.Imaging (box 10) would be performed as an early step in the embolizationprocedure, followed by the selection of one of the standardized implantdevices. This and other variations and modifications are consideredwithin the spirit and scope of the invention, as described in the claimsthat follow.

What is claimed is:
 1. A vascular implant device for embolizing avascular site, the device having a compressed configuration from whichit is expansible into an expanded configuration substantially conformingto the shape and size of the vascular site.
 2. The vascular implantdevice of claim 1 , wherein the implant device has an initialconfiguration in which it is in the form of a scaled down model of thevascular site, and from which it is compressible into the compressedconfiguration.
 3. The vascular implant device of claim 2 , wherein thedevice is formed of a hydrophilic foam material.
 4. The vascular implantdevice of claim 3 , wherein the foam material is a macroporous hydrogelfoam material.
 5. The vascular implant device of claim 1 , wherein theimplant device is compressible into its compressed configuration fromits expanded configuration.
 6. The vascular implant device of claim 5 ,wherein the device is formed of a substantially non-hydrophilicpolymeric foam material.
 7. The vascular implant device of claim 1 ,wherein the device is radiopaque.
 8. A method of manufacturing avascular implant device for embolizing a vascular site, comprising thesteps of: (a) imaging a vascular site by scanning the vascular site tocreate a digitized scan data set; (b) creating a three-dimensionaldigitized virtual model of the vascular site using the scan data set;and (c) forming a vascular implant device in the configuration of aphysical model of the vascular site, using the virtual model, theimplant being formed from a compressible foam material.
 9. The method ofclaim 8 , wherein the forming step comprises the steps of: (c)(1)creating a three-dimensional physical mold of the vascular site usingthe virtual model; and (c)(2) molding a vascular implant in theconfiguration of a physical model of the vascular site.
 10. The methodof claim 9 , wherein the physical mold created in the step of creatingthe physical mold is a scaled-down physical mold.
 11. The method ofclaim 10 , wherein the implant molded in the molding step is in the formof a scaled-down physical model of the vascular site.
 12. The method ofclaim 8 , wherein the imaging step is performed by a technique selectedfrom the group consisting of computer tomography, magnetic resonanceimaging, magnetic resonance angiography, and ultrasound.
 13. The methodof claim 8 , wherein the step of creating a virtual model is performedby a computer program.
 14. The method of claim 9 , wherein the step ofcreating the mold is performed by a CAD/CAM program.
 15. The method ofclaim 14 , wherein the step of creating the mold is performed bystereolithography controlled by the CAD/CAM program.
 16. The method ofclaim 11 , wherein the compressible foam material includes ahydrophilically expansible foam material.
 17. The method of claim 16 ,wherein the foam material includes a macroporous hydrogel foam material.18. The method of claim 9 , wherein physical mold created in the step ofcreating a physical mold is a substantially full size replica of thevascular site.
 19. The method of claim 18 , wherein the implant moldedin the molding step is a substantially full size model of the vascularsite.
 20. The method of claim 19 , wherein the compressible foammaterial includes a substantially non-hydrophilic polymeric foammaterial.
 21. A method of embolizing a vascular site, comprising thesteps of: (a) providing a vascular implant in the form of a physicalmodel of the vascular site, the implant being formed of a moldable,compressible foam material; (b) compressing the implant into acompressed configuration; (c) deploying the implant in a vascular sitewith a microcatheter, while the implant is in its compressedconfiguration; and (d) expanding the implant in situ substantially tofill the vascular site.
 22. The method of claim 21 , wherein the implantis in the form of a scaled-down model of the vascular site, and whereinthe implant is formed of a hydrophilically-expansible foam material. 23.The method of claim 22 , wherein the expanding step is performed by thehydrophilic absorption of fluid by the implant.
 24. The method of claim21 , wherein the deploying step comprises the steps of: (c)(1) insertingthe distal end of the microcatheter into the vascular site; (c)(2)passing the implant through the microcatheter, while the implant is inits compressed configuration, until the implant emerges from the distalend thereof into the vascular site; and (c)(3) releasing the implant,while in its compressed configuration, from the distal end of themicrocatheter.
 25. Apparatus for embolizing a vascular site, comprising:a microcatheter having a distal end and a proximal end; a vascularimplant device configured as a model of the vascular site and formed ofa compressible foam material, the implant device having a compressedconfiguration dimensioned to pass through the microcatheter from theproximal end thereof and out of the distal end thereof; a retentionelement contained within the microcatheter and having a distal enddetachably connected to the implant device; and a deployment elementoperably associated with the retention element and engageable againstthe implant device so as to separate the implant device from theretention element when the implant device has emerged from the distalend of the microcatheter.
 26. The apparatus of claim 25 , wherein thedeployment element is dimensioned to pass axially through themicrocatheter from the proximal end to the distal end thereof, thedeployment element having a distal end that is engageable against theimplant device; and wherein the retention element is movable with thedeployment element when the deployment element is passed through themicrocatheter, and is also movable between first and second positionsrelative to the distal end of the deployment element, whereby theimplant device is displaced out of the distal end of the microcatheterwhen the deployment element is passed through the microcatheter, andwhereby the implant device is separated from the retention element whenthe retention element is moved from the first position to the secondposition.
 27. The apparatus of claim 25 , wherein the implant device isinitially configured as a scaled-down model of the vascular site and hasan expanded configuration in which its substantially conforms to thevascular site.
 28. The apparatus of claim 27 , wherein the implantdevice is formed of a hydrophilic, macroporous, polymeric foam material.29. The apparatus of claim 25 , wherein the deployment element comprisesan elongate, flexible, tubular element.
 30. The apparatus of claim 29 ,wherein the retention element comprises an elongate, flexible,filamentous element disposed axially through the tubular element andmovable with respect thereto between the first and second positions.